We are studying the organization and expression of SV40 and adenovirus 2 genomes contained in Ad2-SV40 hybrid virus DNA molecules. The hybrid viruses are also used as models for understanding the behavior of integrated genomes. We are also analyzing the behavior of SV40 and Ad2-transformed cells (and somatic cell hybrids of these parents) as a function of the molecular conformation of viral nucleic acids within these cells, as a function of events which may control (or be controlled by) viral replication, transcription, and translation, and as a function (in vivo) of host immune recognition and killing. Secondly, we are analyzing the state and expression of the endogenous AKR murine leukemia virus genome in mice with varying expression of leukemia and virus production, as well as exploring the evolution, transmission, and relation to leukemogenesis of various murine RNA viruses. The techniques of restriction endonuclease mapping and molecular cloning are being applied to this genetic analysis of ecotropic, xenotropic, amphotropic, and recombinant murine leukemia viruses.